From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DE045429CC2 for ; Wed, 12 Aug 2026 11:50:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786535423; cv=none; b=JX62s/43Ia7+GYXJ3wuqxlMYUOp6PXhV3y4tPygzmgY972rlt36TsHVUK0ZU2oSdka1m0/3EDnVA5HCNc/A9CgaaXf0KhElo/vlaQp5Z8XRHGjW6P3O7ne0yb1yxVBaDkYVdkDGlpki8g6ouok+JcsSKEIHvm7Y1yoCc+nWwArc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786535423; c=relaxed/simple; bh=CZkqwJ3Ji2mponkpxPLnnh1/tsyS8H5PHEpNwEFQkSQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=T51iWgkS6aCrSicFJX4jbqfptt3lD+zEW2bdEsQlBbn8JHZdHez5VSb5aKII1NyS90fL4rZ2ulVlzCkiXyVwkJgxPKRFuqwBczQmsCk7QyYqz1QMu3+yA1ZfOSEOsfyz+yFw7u0lkERkiNFr4w+Odj7WGn46Jok6piG9UbutnSQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B1/yfaby; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="B1/yfaby" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B17A91F00A3E; Wed, 12 Aug 2026 11:50:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786535421; bh=NzD8EjbNfwxWOr824IoqhG8JtzqQbE0vxinz7zy2JJg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=B1/yfabyBjcixN4UA0vcVlXQ0twNP3kOpUIfZrRJ5Fu2xVyX3ggAcZfXZeCmhYKxl naEE2DNROhkFbIb/vR3yZKYZ/W16PeVLE4tTZ9DdGiTW3YpFbsR7KZipVdPgDgNecq QSGD2TN/HT+6CrE8Y0Kc/vx7WxFRUvAU9VzDReOchwM/BNC7M3JEGS/JwQ2KaJ7DrI z9Dee90kEEgtpIAeqxYMWt8AK6iUNzezWHkbgETqVUvZoDSa6jcY74aG1DSMuyhnxF BjNcg9JXXNIbYxVCflZeR67OdQg3/1g6UqFg6KjrD8AbNK4S9ZzuIey/F5H1vB2SCL a7lhdpe4PNYqw== Message-ID: <8a9d5a6f-a7c6-468f-8b50-a7aa2b4dea2c@kernel.org> Date: Wed, 12 Aug 2026 13:50:17 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 3/8] mm/gup: split follow_page_pte_commit() out of follow_page_pte() To: Rik van Riel , linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , linux-mm@kvack.org References: <20260811025157.1632867-1-riel@surriel.com> <20260811025157.1632867-4-riel@surriel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/11/26 04:51, Rik van Riel wrote: > follow_page_pte() does two things once it has resolved a present PTE > to a page: run the per-PTE safety checks (write-fault, unshare), then > commit to that page: grab a ref, fault it in if pinning, mark it > dirty/accessed, and hand it back to the caller. > > Split the second part into its own follow_page_pte_commit(), unchanged > except for taking its inputs as parameters instead of local variables, > so the checks and the commit can be applied at different granularities. > > No functional changes intended. > > Suggested-by: David Hildenbrand > Assisted-by: Claude:claude-opus-4-8 > Signed-off-by: Rik van Riel > --- > mm/gup.c | 78 +++++++++++++++++++++++++++++++++++--------------------- > 1 file changed, 49 insertions(+), 29 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index e4e6d0993424..b755ceaac0f5 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -822,6 +822,52 @@ static inline bool can_follow_write_pte(pte_t pte, struct page *page, > return !userfaultfd_pte_wp(vma, pte); > } > > +/* > + * The caller has already run every per-PTE safety check (present, > + * write-fault, gup_must_unshare()) on the PTE, so this only does the > + * per-folio work: the refcount grab, the FOLL_PIN accessibility fault-in, > + * dirty/accessed marking, and the array fill with the cache flush. > + */ If a function needs 4 lines of internal doc to understand what it does, then maybe it's not the right function name or abstraction. :) I don't particularly enjoy the "commit" terminology, it looses the detail of the most important thing this function is supposed to to: grab a folio reference. We're passing in the pte only to do a single pte_dirty(). If the helper is actually what we want, likely we just just pass in the pte_dirty() directly and remove all pte leftovers from the helper. I'd assume that we'd want a function where we can similarly punch in a PMD/PUD and have it do the same thing as well, instead of special-casing ptes. Let me think about this some more, I might have to play with the code myself to understand how this should all be cleaned up. -- Cheers, David